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4. Measurements of Neutron Scattering from a Copper Sample Using a Quasi-Differential Method in the Region from 2 keV to 20 MeV

Author

Blain, E., Danon, Y., Barry, D. P., Epping, B. E., Youmans, A., Rapp, M. J., Daskalakis, A. M., and Block, R. C.

Abstract

AbstractNeutron scattering from a copper sample was measured at Rensselaer Polytechnic Institute utilizing the quasi-differential method. The measurement spanned the energy range from 0.5 to 20 MeV using the high-energy scattering system and from 2 keV to 0.5 MeV using the new mid-energy scattering system. Copper was selected as a material of interest to measure due to large discrepancies between experiments and simulations of the Zeus benchmark. The Zeus benchmark consists of a copper reflected highly enriched uranium system, and the angular distribution of copper scattering was thought to potentially be the cause of the discrepancy. The copper measurements found differences in the scattering response particularly in the incident energy region from 1 to 2 MeV for the high-energy measurement and from 2 to 4 keV in the mid-energy system. These differences are particularly noticeable at angles near 90 deg in the high-energy system and back angles in the mid-energy system. Additionally, for ENDF/B-VIII.0 there is a large discrepancy at the forward angle in the energy range around 0.5 MeV. For these reasons, a new evaluation of copper scattering utilizing these results is recommended and perhaps could help to improve the agreement with the Zeus benchmarks.

Published
2022
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8. Validation of Unresolved Neutron Resonance Parameters Using a Thick-Sample Transmission Measurement

Author

Brown, Jesse M., Block, R. C., Youmans, A., Choun, H., Ney, A., Blain, E., Barry, D. P., Rapp, M. J., and Danon, Y.

Abstract

AbstractOften discrepancies can be found in the corresponding cross sections of different evaluated nuclear data libraries. Traditional integral benchmarks that are used to validate such libraries are sensitive to cross-section values across many different energies. This means an erroneously low cross section at one energy may compensate for an erroneously high cross section at another energy, and the integral benchmark value may still be met. While the evaluated cross section may agree with that single benchmark, it could affect other systems differently. To reduce the potential for this error, an energy differential validation method is proposed herein for continuous energy Monte Carlo neutron transport models in the resolved resonance region and the unresolved resonance region (URR). The proposed method exposes the underlying physics of the URR and validates both the average cross section and resonance self-shielding effect driven by the fluctuations in that cross section. This is done by measuring the neutron transmission of a thick sample that, by its nature, exaggerates the resonance self-shielding effect. This validation method is shown to be very sensitive to the cross-section model used (resolved versus unresolved) and the fluctuation correction employed, allowing it to probe the validity of the previously mentioned cross-section evaluations. Tantalum-181 is used as an example to demonstrate the impact of different resonance evaluations. It was found that the JEFF-3.3 and JENDL-4.0u evaluations made reasonable choices for cross-section models of 181Ta; none of the current evaluations, however, can be used to properly model the validation transmission over all energies. It was also found that updating resonance parameters in the URR provided better agreement with the validation transmission.

Published
2020
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10. Neutron Transmission and Capture Measurements of 133Cs from 0.01 to 600 eV

Author

Block, R. C., Burke, J. A., Barry, D. P., Drindak, N. J., Leinweber, G., Remley, K. E., Ballad, R. V., Rapp, M. J., and Danon, Y.

Abstract

AbstractNeutron capture and transmission measurements were carried out from 0.01 to 600 eV on both solid and liquid samples containing elemental cesium (133Cs). Only s-wave resonances were observed in these measurements. These data were analyzed for resonance parameters utilizing the SAMMY Bayesian analysis code to simultaneously fit both the capture and transmission data. Parameters were obtained for 31 cesium resonances up to 600 eV. The thermal capture cross section and capture resonance integral were determined. The thermal capture cross section is 10% larger than the ENDF, JENDL, and JEFF evaluated values but lies within the uncertainty of the most recent measurement by Yoon and Lee [New Phys.: Sae Mulli (Korean Phys. Soc.)., Vol. 61, p. 7 (2011)]. The capture resonance integral has a statistical 1σ error of 2% and lies 1.4σ above the JENDL value, 5.5σ above the ENDF value, and 3.9σ above the JEFF value. The s-wave strength function was determined.

Published
2019
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13. Simultaneous Measurement of 235U Fission and Capture Cross Sections From 0.01 eV to 3 keV Using a Gamma Multiplicity Detector

Author

Danon, Y., Williams, D., Bahran, R., Blain, E., McDermott, B., Barry, D., Leinweber, G., Block, R., and Rapp, M.

Abstract

AbstractThe neutron microscopic capture cross section for 235U is a critical parameter for the design and operation of nuclear reactors. The evaluated nuclear data libraries of ENDF/B-VII.1 and JENDL-4.0 have nearly identical values for the neutron capture cross section for neutron energies below 0.5 keV. In the most recent release of the JENDL library the onset of the unresolved resonance region was changed from 2.25 keV to 0.5 keV. In the energy region from 1.5 keV to 2.25 keV the average neutron capture cross section from ENDF/B-VII.1 is about 10% higher than that from JENDL-4.0. In an attempt to address the discrepancies between the libraries, a measurement of the neutron capture cross section of 235U was conducted at the Gaerttner LINAC Center located at Rensselaer Polytechnic Institute. This measurement used a 16-segment -multiplicity NaI(Tl) detector to detect the prompt gammas emitted from neutron interactions with a highly enriched 235U sample. Using the time-of-flight method, detected events were recorded and grouped based on the total gamma energy per interaction and observed multiplicity. A method was developed to separate fission from capture based on total energy deposition and gamma multiplicity. Application of this method in the thermal and resonance region below 0.5 keV for both the fission and capture produced cross sections that are in good agreement with both ENDF/B-VII.1 and JENDL-4.0 evaluations. The measurements support a lower 235U neutron capture cross section in the energy range 0.5 to 2.25 keV, which is closer to JENDL 4.0.

Published
2017
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18. Neutron Capture and Transmission Measurements and Resonance Parameter Analysis of Niobium

Author

Drindak, N. J., primary, Burke, J. A., additional, Leinweber, G., additional, Helm, J. A., additional, Hoole, J. G., additional, Block, R. C., additional, Danon, Y., additional, Slovacek, R. E., additional, Moretti, B. E., additional, Werner, C. J., additional, Overberg, M. E., additional, Kolda, S. A., additional, Trbovich, M. J., additional, and Barry, D. P., additional

Published
2006
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35. Corrigenda

Author

Bartolome, Z. M., primary, Hockenbury, R. W., additional, Moyer, W. R., additional, Tatarczuk, J. R., additional, and Block, R. C., additional

Published
1970
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